Force networks in shear thickening suspensions

The strong shear thickening exhibited by near-hard sphere suspensions has features of a phase transition, with strong fluctuations of the stress at fixed shear rate in the vicinity (with respect to both solid fraction and shear rate) of the onset of shear thickening. In our studies based on simulations which capture the viscous-to-frictional rheology transition, a notable feature is that the high- and low-stress states do not show significant differences in typical measures of their spatial correlation: e.g., the pair distribution function differs only slightly between the two. However, the contact force networks that develop as the result of shear stress driving particles into contact against an opposing repulsive interparticle force show distinct changes across this transition, and their statistics give insight to the features that allow a single volume fraction to offer remarkably different resistance to flow, from smoothly flowing at small stress to very viscous or even fully jammed at high stress. Results from persistent homology tools, k-core analysis, and tools of statistical mechanics will be presented to elucidate some new features of dense suspension shear thickening.